As is well known, delay networks are extensively used in most of electronic circuits operated either at low or high voltage levels.
In particular, delay networks are known which employ semiconductor devices implemented with CMOS technology and operated in their saturation range. However, the charge/discharge currents, I.sub.sat, of such devices--and with them the propagation delays provided by such conventional delay networks--are tied in a quadratic fashion to the supply voltage Vdd by the following relationship: EQU I.sub.sat =K*(1/2)*(Vdd-Vth).sup.2 (1)
where,
K is a multiplicative constant, and PA1 Vth is a threshold voltage.
It will be appreciated from (1) above that, at high levels of the supply voltage Vdd, these conventional delay networks are too fast, to the point of having the effectiveness of their action compromised. In fact, in applications of noise suppression, for example, conventional delay networks are liable to provide delay in diminishing amounts at high voltages, with resulting reduced filtering capability. Due to the presence of elevated levels of voltage and, therefore, of noise this is where the delay is most needed. Thus, in order to achieve a sufficiently delayed propagation for such delay networks to be useful with high voltage levels the amounts of delay provided thereby must be increased. However, this increase produces unacceptable delays at lower voltage levels.
Accordingly, delay networks are needed which have a propagation delay substantially unaffected by operating conditions, and which is specifically independent of the supply voltage Vdd.
This would further the construction of circuits incorporating delay networks, within the frame of their specifications.
Another pressing demand is for delay networks which provides different propagation responses to the switching edges, rising and falling, of a trigger signal, and produces delay in a controllable fashion.
Of particular interest would be the implementation of an asymmetrical delay network having a controllably delayed propagation with respect to a first edge of the trigger signal and a substantially immediate propagation with respect to a second edge thereof.
An asymmetrical delay network would then be available for the construction of a pulse generator adapted to act upon one edge only of two independent trigger signals.
Conventional pulse generators employ delay networks for setting the pulse duration, this duration also being unsuitable at high voltage levels due to its quadratic dependence on the supply voltage Vdd, as determined by relationship (1) above.
One of the underlying technical problems of this invention is to provide an asymmetrical delay network having a significant delay which is substantially independent of the supply voltage with respect to a first edge of a trigger signal, and which offers immediate and natural propagation at a second edge, thereby overcoming the limitations of conventional delay networks.